As well understood in the art, flash illumination apparatus as used with photographic cameras is of two general types. One is an electronic flash device, which has come into widespread use in recent years. The electronic flash has no time lag in starting. It reaches peak illumination instantly when the necessary firing potential is applied, and the flash usually lasts about 0.5 milliseconds after ignition has occurred. The other general type of flash apparatus, much older than the electronic flash but still widely used, is the flash apparatus employing a current-ignited combustion flash light lamp or bulb. The combustion type of flash apparatus has an appreciable time lag of several milliseconds between the time that the firing current is applied to the bulb and the time that peak illumination is reached. The combustion flash has an average duration of about 37 milliseconds, but only part of this is at the peak illumination intensity.
It is very desirable that a camera be usable with both types of flash apparatus, since some potential users of the camera may have flash apparatus of one type, and some may have flash apparatus of the other type. Many cameras are known in the art, which provide so-called "fall" synchronization, so as to be usable with both types of flash apparatus. Most if not all of these cameras of the prior art have two separate synchronized contacts (plug receptacles) usually known in the art as the X contact or receptacle, and the M contact or receptacle. When the camera is being used with an electronic flash unit, the unit is plugged into the X contact, and the mechanism in the camera gives an impulse to this contact at a time when the shutter is completely open. When flash apparatus of the current-ignited combustion lamp type is used, this is plugged into the M contact of the camera, and the camera gives an impulse to this contact at which may be called a pre-ignition time, sufficiently far in advance of full opening of the shutter to allow for the time lag of a few milliseconds between the firing of the combustion flash lamp and the achieving of peak illumination.
The arrangement of two separate ignition devices for the respective flash types is undesirable because it requires a greater complexity and elaborateness, entailing higher cost, and especially because of the unfavorable effect on the aim of keeping the camera as small as possible. With growing trend toward very small cameras, it is simply not possible, as a practical matter, to accommodate two separate ignition devices, so that the camera designer must confine himself to synchronizing mechanism capable of firing only one of the two above mentioned types of flash apparatus.
It has been suggested that a camera equipped with only an X contact could be used to fire a combustion flash lamp, but because of the time lag inherent in a combustion flash bulb, this can be done only with a relatively long exposure. It is usually not possible to use a shutter speed faster than about 1/30 th of a second, if a combustion flash bulb is to be ignited from an X contact. However, an exposure time of this length is often too long to avoid movement blurs, and also it is not practical when the flash is to be used for "fill-in" or shadow-softening purposes, with adequate illumination.
The object of the present invention is to provide full synchronization mechanism capable of use at will, either with a flash bulb or lamp of the current-ignited combustible type, or with an electronic flash unit, full synchronization being achieved with only a single synchronizing device or mechanism, and having only a single synchronous contact (receptacle for receiving a connection plug), and without necessitating any special switching arrangement to switch over from one type of synchronization to the other.
According to the present invention, this object is achieved by providing synchronizing mechanism which applies to the single synchronous contact a first voltage variation which provides the ignition impulse for a combustion lamp, and subsequently applies to the synchronous contact a second voltage variation which provides the ignition impulse for an electronic flash unit. When a combustible flash bulb and its appropriate adapter are plugged into the synchronous contact, the first voltage variation will fire the combustible bulb at a pre-ignition time which makes allowance for the above mentioned illumination lag. When an electronic flash device and its appropriate adapter are plugged into the synchronous contact, the arrangement is such that the first voltage variation will not cause firing of the electronic flash, but the second voltage variation, occuring at a time when the shutter is fully open, will fire the electronic flash.
In a further development of the invention, the synchronizing mechanism of the kind just mentioned is especially designed for use with an electronically controlled diaphragm shutter, in which the opening blade mechanism serves the function of a diaphragm as well as a shutter, and in which a separate blade mechanism closes the exposure aperture or light passage to terminate the exposure. One example of such a shutter is disclosed in the above mentioned Waaske patent application, Ser. No. 466,817. One aspect of the present invention includes automatic flash limitation means.
According to another aspect of the invention, the synchronizing mechanism is so designed that it may be used either for what may be called pure flash photographs (when there is not sufficient illumination for taking the photograph except with the use of flash) and for fill-in or shadow-softening photographs (when there is adequate illumination for taking the picture, but supplemental flash is desired to fill in the deep shadows). In the preferred embodiment of the invention, the synchronizing mechanism includes electronic controls responsive to light reflected from the subject being photographed, and effective to control the exposure both when pure flash and when fill-in flash is used.